This invention relates in general to backing rings for the bearings on railroad axles and, more particularly, to stabilized backing rings that fit axles of varying diameter.
The typical bearing for a railcar fits around a journal at the end of a railcar axle where it is captured between a backing ring and an end cap. The backing ring seats against a fillet that merges into an enlarged dust guard diameter, while the end cap fits over the end of the journal to which it is secured with cap screws. On most journals seal wear rings fit between the bearing and the backing ring and also between the bearing and the end cap. Seals encircle the wear rings and exclude contaminants from the bearing. When tightened, the cap screws bear down against the end cap and clamp the bearing securely between the backing ring and end cap. This forces the backing ring snugly against the fillet.
The journals on any rail car axle represent the regions of least diameter in the axle, yet it is through these journals and nearby dust guard diameters, which are somewhat larger, that the weight of the rail car is transferred to the wheels. Being subject to considerable weight, the journals flex cyclically as wheels roll along the rails of a railroad track, with most of the flexure occurring near the small ends of the fillets. The flexure produces fretting between the backing ring and the fillets, and as a consequence both experience wear. When water seeps into the spaces between the backing rings and the fillets, it exacerbates the fretting with corrosion. Sometimes the wear at a journal is enough to eliminate the clamp fit that holds the bearing in place, and this disturbs the setting for the bearing, imparting more end play than desired. Over the years the Association of American Railroads (AAR) has increased the allowable gross rail load on the 100-ton nominal capacity rail car, which is used bulk commodity transport, from 56427 newtons (25100 lbs) to 59125 newtons (263000 lbs.) in 1961 and then to 64295 newtons (286000 lbs) in 1990. This contributed to axle flexing of a higher magnitude which in turn led to greater fretting wear.
To combat fretting wear and corrosion at axle fillets, bearing manufacturers introduced the fitted backing ring. It had an annular lip which extended axially over the dust guard diameter adjacent to the fillet. Moreover, the AAR set standards for the fitted backing rings and further specified a tolerance for the dust guard diameters so that an interference fits would exist between the dust guard diameters and the annular lips of the backing rings. Thus, a fitted back ring required the application of some force during the last increment of installation, this to overcome the interference fit. The press-fit stiffened the joint between the backing ring and the fillet on the journal and excluded moisture, thus reducing both fretting and corrosion between the backing ring and the journal. However, the MR specified larger dust guard diameters for the new axles—dust guard diameters larger than those on older traditional axles. This enabled the new fitted backing rings to be used interchangeably with the old traditional axles and the new axles, but without interference fits on the older axles. In the absence of an interference fit, a fitted backing ring possesses little, if any, advantage over a more traditional backing ring without a lip.